During the building of a new structure it is common practice to provide systems for insulating the foundations and the portions of masonry that are in contact with the ground, in order to avoid infiltrations and/or the capillary rise of water. Elastomeric sheets, in roll form or liquid form, laid between the structure and the ground, are normally used.
If these systems have not been provided or if their functionality over time is compromised, infiltrations of water may occur or damp stains may appear due to the impregnation by capillary action of the building materials.
The retrofitting of a waterproofing system or the restoration of the functionality of an existing system is a rare practice due to the operating difficulties that arise from it.
Indeed, if one wished to intervene from the outside, one would have to perform excavations along the entire perimeter of the wall in order to be able to position or restore the installation. Nevertheless, it would not be possible to ensure the waterproofing of the flooring.
Placing the insulation on the internal surfaces would block infiltrations but not capillary rise in the wall. This type of waterproofing would entail in any case, in most cases, the removal of surface coverings (tiles, plasters, . . . ).
Similar problems occur also in other civil structures, such as for example tunnels, containment walls, underground tanks.
Methods for waterproofing after building by means of injections have already been used for years. They can be performed both within the wall face to be waterproofed, in order to saturate the voids that are present, and behind said wall face, in order to create a waterproofing barrier between the wall and the ground.
The products used can be of different types, for example polyurethane resins, acrylic resins or silicate mixtures.
The injections performed behind the wall are performed in the following steps of operation:                perforation of the masonry:        placement of plugs in the holes (to avoid the outflow of the injected material);        execution of the injections, starting from the areas located at lower heights and proceeding by successive horizontal alignments toward the top of the wall face.        
The injected products, initially in the liquid state, harden in more or less short times and become waterproof. The times required for the injected mixture to pass from the liquid state to the solid state are a function of the type of reagents used. They can vary from a few seconds, as in the case of polyurethane resins, to a few hours for silicate mixtures.
With reference to injections of polyurethane resins, it is noted that they have excellent mechanical properties, short reaction times, high initial viscosities of the mixture and the possibility of expanding their initial volume during the hardening reaction.
This makes it possible to achieve good results if there is a cracked containment wall in which it is necessary to block substantial water seepage.
However, the main drawbacks of processes that use polyurethane resins are the cost of the raw material and the need to use rather expensive equipment.
Moreover, since these resins expand very quickly, one cannot be sure that they are able to permeate the smaller voids.
On the other hand, the injection of silicate mixtures is characterized by extremely well adjustable reaction times, by low initial viscosity of the mixture, by much lower costs of the raw material with respect to polyurethane resins, and by the fact that they require simplified and less expensive injection systems.
However, it is observed that waterproofing by means of silicate mixtures is ineffective if even just one portion of the containment wall to be waterproofed is cracked or subject to substantial seepage of water, since this would cause the mixture to be washed out in a very short time, which would lead to the consequent restoration of the initial situation of infiltrations if they are injected into the entire wall.
Furthermore, the extremely low viscosity of silicate mixtures at the time of their injection into the ground makes it very difficult to check their adhesion to the entire surface of the underground wall that must be subjected to waterproofing.